Ionospheric Weather at Two Starlink Launches during Two-Phase Geomagnetic Storms

The launch of a series of Starlink internet satellites on 3 February 2022 (S-36), and 7 July 2022 (S-49), coincided with the development of two-phase geomagnetic storms. The first launch S-36 took place in the middle of the moderate two-phase space weather storm, which induced significant technological consequences. After liftoff on 3 February at 18:13 UT, all Starlink satellites reached an initial altitude of 350 km in perigee and had to reach an altitude of ~550 km after the maneuver. However, 38 of 49 launched spacecrafts did not reach the planned altitude, left orbit due to increased drag and reentered the atmosphere on 8 February. A geomagnetic storm on 3–4 February 2022 has increased the density of the neutral atmosphere up to 50%, increasing drag of the satellites and dooming most of them. The second launch of S-49 at 13:11 UT on 7 July 2022 was successful at the peak of the two-phase geomagnetic storm. The global ionospheric maps of the total electron content (GIM-TEC) have been used to produce the ionospheric weather GIM-W index maps and Global Electron Content (GEC). We observed a GEC increment from 10 to 24% for the storm peak after the Starlink launch at both storms, accompanying the neutral density increase identified earlier. GIM-TEC maps are available with a lag (delay) of 1–2 days (real-time GIMs have a lag less than 15 min), so the GIMs forecast is required by the time of the launch. Comparisons of different GIMs forecast techniques are provided including the Center for Orbit Determination in Europe (CODE), Beijing (BADG and CASG) and IZMIRAN (JPRG) 1- and 2-day forecasts, and the Universitat Politecnica de Catalunya (UPC-ionSAT) forecast for 6, 12, 18, 24 and 48 h in advance. We present the results of the analysis of evolution of the ionospheric parameters during both events. The poor correspondence between observed and predicted GIM-TEC and GEC confirms an urgent need for the industry–science awareness of now-casting/forecasting/accessibility of GIM-TECs during the space weather events.


Introduction
Knowledge of the state of the global ionosphere presents an indispensable tool in the planning and operation of space experiments. An example of such space activity is the Starlink satellite network developed by the private spaceflight company SpaceX to provide low-cost internet access to remote locations. In view of increasing solar activity during recent and forthcoming years approaching the peak of the solar cycle 25, the satellites started sinking toward the atmosphere at an unusually fast rate-up to 10 times faster than before [1]. Satellites orbiting close to Earth always face the drag of the residual atmosphere, which gradually slows the spacecraft and eventually makes them fall back to the planet.
Such an event occurred with the Starlink launch on 3 February 2022 (S-36), which happened in the middle of the moderate two-phase space weather storm [2]. After liftoff on turbance (red area) is most essential, for example, during the peaks of the geomagnetic storm. The negative storm effects (blue area) are observed over the Antarctic region at the time approaching the storm peaks and became dominant after the 2nd storm peak. Note that the GIM-TEC and GIM-W maps could not be examined in real time during the Starlink operation: they are produced with 1 or 2 days' lag (delay) after the space weather event when the GIMs became available, so these GIMs can be used only for the postprocessing analysis.    Figure 1a provided by OMNI from 6 to 9 July 2022. The Starlink S-49 launch at 13:11 UT on 7 July (thick vertical line) occurred two hours later than the storm onset which is close to the 1st peak of the proton density (Np = 56.84 cm −3 at 11:25 UT on 7 July). The geomagnetic storm shows gradual development during 15 h of the main phase ending with the 1st peak SYM-H = −85 nT at 02:15 UT on 8 July, and the 2nd less intense peak was observed with SYM-H = −42 nT at 11:35 UT on 8 July. The gradual development of the geomagnetic storm is accompanied by a quiet GIM-W index (Figure 2b, at 00:00 and 12:00 UT on 7 July). The positive GIM-W enhancement is dominant around the peak of SYM-H (00:00 UT on 8 July), then it is confined at the southern hemisphere towards the storm recovery of SYM-H at 12:00 UT on 8 July. The increased negative W index effects in the northern hemisphere are gradually replaced by the negative storm in the southern hemisphere. Again, these GIMs can be used only for the postprocessing analysis, because they are produced with a lag of 1-2 days from the relevant GIM-TECs. While we observe the local or regional features of the near-Earth plasma on the global GIMs, an advantage of the global electron content (GEC) is the presentation of the state and variability of the ionosphere as a whole. At a given time, the global electron content depends on 3-D electron density distribution, in terms of latitude, longitude and height, integrated over the volume of the ionosphere and plasmasphere from the surface of the Earth to the altitude of GPS satellites [26]. Calculation of the GEC proxy is based on GIM-TEC maps available in latitude φ from 87.5° S to 87.5° N in steps of Δφ = 2.5°, longitude λ from 180° W to 180° E in steps of Δλ = 5°. Individual grid values TEC (φi,λj) from GIM are used to produce GEC with Equation (1): , The surface area coefficient Si(φi) for the cells centered at grid [φi,λj] depends on latitude φi and step in longitude Δλ: with Figure 2. The same as Figure 1a,b but from 6 to 9 July 2022 related with the Starlink S-49 launch at 13:11 UT on 7 July. The interplanetary magnetic field (IMF) 5 min parameters provided by OMNI are plotted in Figure 1a from 2 to 5 February 2022. Here, we observe from top to bottom: the IMF magnetic field magnitude B, in nT; the field's southward component Bz, in nT, in the GSM coordinate system; the solar wind speed Vsw, in km/s; the proton density Np, in cm −3 ; the plasma temperature Tp, in K; and the equatorial geomagnetic SYM/H index, in nT. The Starlink S-36 launch (thick vertical line) at 18:13 UT on 3 February 2022 occurred between the 1st peak of the geomagnetic storm (symmetric ring current index SYM-H = −80 nT at 10:55 UT on 3 February) and the 2nd peak (SYM-H = −70 nT at 20:40 UT on 4 February). Note that only one peak is observed in the Tp temperature profile at 11:15 UT on 3 February 2022. Selected GIM-W index maps derived from 15 min tomographic-kriging, UPC rapid GIM (UQRG) GIM-TECs are plotted in Figure 1b for 00:00 and 12:00 UT on 3, 4 and 5 February. The global spatial distribution of W index includes quiet conditions at the prestorm hour 00:00 UT on 3 February. An enhanced positive TEC disturbance (red area) is most essential, for example, during the peaks of the geomagnetic storm. The negative storm effects (blue area) are observed over the Antarctic region at the time approaching the storm peaks and became dominant after the 2nd storm peak. Note that the GIM-TEC and GIM-W maps could not be examined in real time during the Starlink operation: they are produced with 1 or 2 days' lag (delay) after the space weather event when the GIMs became available, so these GIMs can be used only for the postprocessing analysis. Figure 2a presents IMF parameters similar to Figure 1a provided by OMNI from 6 to 9 July 2022. The Starlink S-49 launch at 13:11 UT on 7 July (thick vertical line) occurred two hours later than the storm onset which is close to the 1st peak of the proton density (Np = 56.84 cm −3 at 11:25 UT on 7 July). The geomagnetic storm shows gradual development during 15 h of the main phase ending with the 1st peak SYM-H = −85 nT at 02:15 UT on 8 July, and the 2nd less intense peak was observed with SYM-H = −42 nT at 11:35 UT on 8 July. The gradual development of the geomagnetic storm is accompanied by a quiet GIM-W index (Figure 2b, at 00:00 and 12:00 UT on 7 July). The positive GIM-W enhancement is dominant around the peak of SYM-H (00:00 UT on 8 July), then it is confined at the southern hemisphere towards the storm recovery of SYM-H at 12:00 UT on 8 July. The increased negative W index effects in the northern hemisphere are gradually replaced by the negative storm in the southern hemisphere. Again, these GIMs can be used only for the postprocessing analysis, because they are produced with a lag of 1-2 days from the relevant GIM-TECs.
While we observe the local or regional features of the near-Earth plasma on the global GIMs, an advantage of the global electron content (GEC) is the presentation of the state and variability of the ionosphere as a whole. At a given time, the global electron content depends on 3-D electron density distribution, in terms of latitude, longitude and height, integrated over the volume of the ionosphere and plasmasphere from the surface of the Earth to the altitude of GPS satellites [25]. Calculation of the GEC proxy is based on GIM-TEC maps available in latitude ϕ from 87.5 • S to 87.5 • N in steps of ∆ϕ = 2.5 • , longitude λ from 180 • W to 180 • E in steps of ∆λ = 5 • . Individual grid values TEC (ϕ i , λ j ) from GIM are used to produce GEC with Equation (1): The surface area coefficient S i (ϕ i ) for the cells centered at grid [ϕ i , λ j ] depends on latitude ϕ i and step in longitude ∆λ: with The coefficients are determined according to the geocentric distances of the TEC receiver and the ionospheric pierce point (in our case, the Earth's radius R E = 6370 km plus height h = 450 km). The total number of coefficients S i (ϕ i ) is equal to 71 (ϕ i = −87.5, −85, . . ., 87.5 • N), which are calculated a priori and applied with Equation (1) to different GIMs.  (1) and (2)); (ii) appreciable periods of enhanced/depleted GEC. The Starlink launches (marked with a star) are observed during the moderate geomagnetic storms (denoted with white lines). Every pixel in the images of Figure 3a,b is derived from a separate GIM, so that GEC presents a metrics reducing the GIM's data set by the number of pixels in one GIM, i.e., 5112 times based on the information in the paper.
The coefficients are determined according to the geocentric distances of the TEC receiver and the ionospheric pierce point (in our case, the Earth's radius RE = 6370 km plus height h = 450 km). The total number of coefficients Si(φi) is equal to 71 (φi = −87.5, −85, …, 87.5° N), which are calculated a priori and applied with Equation (1) to different GIMs.
Hour-by-hour GEC calculations with the above equations from the hourly UPC tomographic-kriging GIM 'UQRG' (0, 1, …, 23 UT) for February 2022 ( Figure 3a) and July 2022 ( Figure 3b) reveal two features of GEC variation: (i) missing diurnal GEC variation because the local time changes are masked by latitudinal−longitudinal map summation (Equations (1) and (2)); (ii) appreciable periods of enhanced/depleted GEC. The Starlink launches (marked with a star) are observed during the moderate geomagnetic storms (denoted with white lines). Every pixel in the images of Figure 3a,b is derived from a separate GIM, so that GEC presents a metrics reducing the GIM's data set by the number of pixels in one GIM, i.e., 5112 times based on the information in the paper. Daily-hourly GEC variation produced from the different GIMs during February 2022 are plotted in Figure 4a-d. The variation of geomagnetic Apo index equivalent to the Kp index but on an hourly cadence [31] and Dst index [32] during February 2022 are plotted in Figure 4e,f, respectively. The Starlink S-36 launch is shown with a thick vertical line. The JPLR-based GEC is provided in all four panels for comparison with other data. The difference between JPLR 'true' GEC and 1-and 2-day JPLR-based forecast by IZ-MIRAN (JPLR1 and JPLR2) [10] brought to light some differences, as they can be seen in Figure 4a. Similar differences are observed between CODE 'true' data and CODE1/CODE2 forecast ( Figure 4b) [12], CASG 'true' data and CASG1/CASG2 forecast ( Figure 4c) [14], and BUAG 'true' and B1PG/B2PG forecast (Figure 4d) [13]. The UPC-IonSAT produces UQRG and real-time UADG on a 15 min cadence [16,28], but only hourly GEC derived from them are used in the present study, similar to other kinds of 'true' GIMs. Note the close resemblance of hourly UQRG and real-time UADG-based results (Figure 4a) but the difference of their 'true' profiles from JPLR, which is also seen for CODE (Figure 4b  Daily-hourly GEC variation produced from the different GIMs during February 2022 are plotted in Figure 4a-d. The variation of geomagnetic Apo index equivalent to the Kp index but on an hourly cadence [30] and Dst index [31] during February 2022 are plotted in Figure 4e,f, respectively. The Starlink S-36 launch is shown with a thick vertical line. The JPLR-based GEC is provided in all four panels for comparison with other data. The difference between JPLR 'true' GEC and 1-and 2-day JPLR-based forecast by IZMIRAN (JPLR1 and JPLR2) [10] brought to light some differences, as they can be seen in Figure 4a. Similar differences are observed between CODE 'true' data and CODE1/CODE2 forecast ( Figure 4b) [12], CASG 'true' data and CASG1/CASG2 forecast (Figure 4c) [14], and BUAG 'true' and B1PG/B2PG forecast (Figure 4d) [13]. The UPC-IonSAT produces UQRG and real-time UADG on a 15 min cadence [16,27], but only hourly GEC derived from them are used in the present study, similar to other kinds of 'true' GIMs. Note the close resemblance of hourly UQRG and real-time UADG-based results (Figure 4a) but the difference of their 'true' profiles from JPLR, which is also seen for CODE (Figure 4b It has been noted that the density of the neutral atmosphere was increased up to 50% during the geomagnetic storm on 3-4 February 2022, increasing drag of the satellites and dooming most of them [2][3][4][5][6][7][8]. To check a possible increase of GEC magnitude during the storm, we compare the peak magnitude GEC max after the Starlink launch with the base daily-average quiet value GEC av on the prestorm day. Table 2 provides these parameters for the different data centers after the Starlink launches on 3 February and 7 July 2022. The increment of the global electron content is calculated in percent, dGECp, with Equation (3):  It has been noted that the density of the neutral atmosphere was increased up t during the geomagnetic storm on 3-4 February 2022, increasing drag of the satellite dooming most of them [2][3][4][5][6][7][8]. To check a possible increase of GEC magnitude duri storm, we compare the peak magnitude GECmax after the Starlink launch with th daily−average quiet value GECav on the prestorm day. Table 2 provides these param for the different data centers after the Starlink launches on 3 February and 7 July The increment of the global electron content is calculated in percent, dGECp, with tion (3):

= 100%
We observe in Table 2 that the GEC increment varies from 10 to 24%, accompa the neutral density increase [2−8] for both events. This characteristic presents a me of the positive GEC intensification for the second phase of the ionosphere storm.  We observe in Table 2 that the GEC increment varies from 10 to 24%, accompanying the neutral density increase [2][3][4][5][6][7][8] for both events. This characteristic presents a measure of the positive GEC intensification for the second phase of the ionosphere storm.
To estimate quantitative agreement/disagreement between the different data, we determine the coefficient of determination (R-squared or R 2 ) as a measure of the difference between the 'true' data (Y) and forecast of GEC (X) or between the different 'true' data (X and Y) [32]: The R 2 varies from −∞ to 1 (worst value = −∞; best value = +1), so R 2 = 1 presents the best resemblance of two data sets. This feature makes it easy to allocate a reasonable agreement with R 2 > 0.5.
The root-mean-square (RMS) deviation (in GECU) is also calculated: The results of R 2 and RMS calculation for the different monthly sets of GEC are provided in Table 3 for February and July 2022. The best agreement between the pairs with R 2 > 0.5 is given in bold. JPLR 'true' profiles show an unacceptable difference with all data reviewed except UQRG in July 2022. Variations of 'true' profiles are very similar, as can be seen in Figure 4, but the absolute values of JPLR GEC are greater than any other 'true' profile. Since Yav (Equation (5)) is calculated from JPLR GEC (the 1st line in Table 3 for February and the 1st line for July), it yields the negative R 2 (Equation (4)), attesting to the poor agreement with other GIMs. Poor R 2 is also obtained for all other indices regarding JPLR GEC in the 1st column of Table 3, when Yav (Equation (5)) is calculated from the other indices. The 'true' data of CODE, BUAG, CASG and UQRG are in agreement during February and July in most cases. The 'true' UQRG and UADG show agreement with 'true' data of other centers except UQRG~JPLR and UADG~UQRG, but they show no agreement with 'forecast' data in February. The agreement is best for UQRG with other data sets in July except for JPLR1 and JPLR2 forecast. The next successful agreement is UADG in July except for JPLR 'true', IZMIRAN 1-and 2-day forecasts of JPLR1 and JPLR2, and CODE d1, BUAG d1 and d2, and CASG d1 and d2 forecasts. Though some 'forecasts' agree with the 'true' UQRG and UADG data, these are not supposed to be used together in practice. In general, there is only one case of the agreement of CASG 'true' data with the relevant 1-day (d1) 'forecast' in July based on GIMs from the same source. At the same time, we observe an agreement between the different 'true'~'true' data pairs, confirming the previous results of comparisons of the different GIMs [27][28][29].
Recognizing that there are no 'true' GEC profiles nor 'true' GIMs by the time of the Starlink launches, we proceed to the evaluation of GIMs forecast by comparison of GEC (as a product of GIM) with 'true' GEC during two storms. The 'true' (Obs.) GEC storm profiles are plotted in Figure 5(a1)-(d1) from 2 February (prestorm day) to 5 February 2022: a1-JPLR, b1-CODE, c1-BUAG, d1-CASG. By the time of the Starlink launch at 18:13 UT on 3 February (thick vertical line), the 'true' data are available only for the prestorm day. The 'base' value presents the average GEC during the prestorm day, 1d-1-day forecast for the day of launch, 2d-2-day forecast for the next day after the launch. The 1d (red) and 2d (green) curves with symbols present the forecast starting on the day of the launch, and similar curves without symbols denote the forecast starting on the next day after the launch when the geomagnetic storm is in progress. The detrended GEC in Figure 5(a2)-(d2) (after subtraction of the base value from GEC 'true' and 'forecast' data) clearly shows two 'true' positive GEC storm phases on 3 and 4 February, followed by the negative phase on 5 February. The positive GEC enhancements occur at the times of the increased neutral atmosphere density, with increased drag dooming most of the Starlink satellites [2][3][4][5][6][7][8]. We note a failure of GEC 'forecast' to outline the 'true' storm effects observed in Figure 5 Similar nonconforming results are obtained between GEC 'true' and 'forecast' profiles plotted from 6 July (prestorm day) to 9 July 2022, including the Starlink S-49 launch at 13:11 UT on 7 July in Figure 6a1-d3. Fortunately, all 53 Starlink S-49 satellites reached this time in their final orbit, because after the failure of S-36 experienced on 3-8 February 2022, the subsequent Starlink launches used a higher initial orbit [2], thereby avoiding a possible drag enhancement. The 'forecast' curves neither reproduce the positive phase of the GEC storm on 7 July and from 00:00 to 05:00 UT on 8 July nor the negative GEC excursion for the rest of the hours on 8 July except for a part of time fit between JPLR~JPLR1 and CODE~CODE1 in the forecast starting one day after the launch, JPLR~JPLR2, CODE~CODE2 and CASG~CASG2 produced on the day of the launch. Similar nonconforming results are obtained between GEC 'true' and 'forecast' profiles plotted from 6 July (prestorm day) to 9 July 2022, including the Starlink S-49 launch at 13:11 UT on 7 July in Figure 6(a1)-(d3). Fortunately, all 53 Starlink S-49 satellites reached this time in their final orbit, because after the failure of S-36 experienced on 3-8 February 2022, the subsequent Starlink launches used a higher initial orbit [2], thereby avoiding a possible drag enhancement. The 'forecast' curves neither reproduce the positive phase of the GEC storm on 7 July and from 00:00 to 05:00 UT on 8 July nor the nega-tive GEC excursion for the rest of the hours on 8 July except for a part of time fit between JPLR~JPLR1 and CODE~CODE1 in the forecast starting one day after the launch, JPLR~JPLR2, CODE~CODE2 and CASG~CASG2 produced on the day of the launch.
Similar nonconforming results are obtained between GEC 'true' and 'forecast' profiles plotted from 6 July (prestorm day) to 9 July 2022, including the Starlink S-49 launch at 13:11 UT on 7 July in Figure 6a1-d3. Fortunately, all 53 Starlink S-49 satellites reached this time in their final orbit, because after the failure of S-36 experienced on 3-8 February 2022, the subsequent Starlink launches used a higher initial orbit [2], thereby avoiding a possible drag enhancement. The 'forecast' curves neither reproduce the positive phase of the GEC storm on 7 July and from 00:00 to 05:00 UT on 8 July nor the negative GEC excursion for the rest of the hours on 8 July except for a part of time fit between JPLR~JPLR1 and CODE~CODE1 in the forecast starting one day after the launch, JPLR~JPLR2, CODE~CODE2 and CASG~CASG2 produced on the day of the launch. The quantitative estimate of a correspondence between the 'true' and 'forecast' GEC storm data with R 2 and RMS using Equations (4)−(6) is presented in Table 4 for the storms on 3−5 February and 7−9 July 2022. There is no reasonable conformity between the forecast (X) and true (Y) data from the four analysis centers all producing R 2 negative results. The quantitative estimate of a correspondence between the 'true' and 'forecast' GEC storm data with R 2 and RMS using Equations (4)-(6) is presented in Table 4 for the storms on 3-5 February and 7-9 July 2022. There is no reasonable conformity between the forecast (X) and true (Y) data from the four analysis centers all producing R 2 negative results. The 'true' UQRG and real-time UADG results are compared with the Nearest-Neighbor (NN) method of 'forecast' for 6, 12, 18, 24 and 48 h in advance [15]. The results are plotted in Figure 7(a1,a2) from 2 February (prestorm day) to 5 February, and in Figure 7(b1,b2) from 6 July (prestorm day) to 9 July 2022. The Starlink launches of S-36 and S-49 are shown by a thick vertical line. An outstanding feature of Figure 7(a1,b2) is the usage of 'true' real-time UADG data observed −15 min prior to the launch with 'forecast' from 6 to 48 h ahead starting afterwards. We see the diversity of NN forecasts, which differ from the 'true' storm profiles failing to fit the positive and negative GEC 'true' excursions. As distinct from Figure 7a1-b2, the same NN forecasts are plotted in Figure 8a1-b2 but using UQRG 'true' data for the day before the launch (prestorm day) and fitting 6, 12, 18, 24 and 48 h 'forecast' starting from 00:00 UT on the day of the launch. Here, 24 h forecast appears to better reproduce part of the positive storm effect on 3 February (blue curve) and 48 h forecast (cyan) closer to approaching part of the 2nd positive storm peak on 4 February. The other options differ from the 'true' storm profiles for both the S-36 and S-49 events.  As distinct from Figure 7(a1)-(b2), the same NN forecasts are plotted in Figure 8(a1)-(b2) but using UQRG 'true' data for the day before the launch (prestorm day) and fitting 6, 12, 18, 24 and 48 h 'forecast' starting from 00:00 UT on the day of the launch. Here, 24 h forecast appears to better reproduce part of the positive storm effect on 3 February (blue curve) and 48 h forecast (cyan) closer to approaching part of the 2nd positive storm peak on 4 February. The other options differ from the 'true' storm profiles for both the S-36 and S-49 events. As distinct from Figure 7a1-b2, the same NN forecasts are plotted in Figure 8a1-b2 but using UQRG 'true' data for the day before the launch (prestorm day) and fitting 6, 12, 18, 24 and 48 h 'forecast' starting from 00:00 UT on the day of the launch. Here, 24 h forecast appears to better reproduce part of the positive storm effect on 3 February (blue curve) and 48 h forecast (cyan) closer to approaching part of the 2nd positive storm peak on 4 February. The other options differ from the 'true' storm profiles for both the S-36 and S-49 events.  The numerical values of R 2 and RMS for the NN 'forecast' (X) are produced using Equations (4)- (6) to estimate their consistency with 'true' UQRG and UADG data (Y) ( Table 5) for the storms on 3-5 February and 7-8 July 2022. Though the better fit of forecast to the 'true' GEC is observed for the part of storm time in Figure 8, the results of Table 5 for the total storm hours during 3-5 February and 7-8 July reveal an appreciable difference between the NN forecast (X) and true (Y) data according to R 2 negative results.

Conclusions
The GIM-TEC global ionospheric maps of the total electron content have been used to produce the ionospheric weather GIM-W index maps and Global Electron Content (GEC). GIM-TEC maps are available with a lag (delay) of 1-2 days (real-time GIMs have a lag of less than 15 min), so the GIMs forecast is required by the time of the launch of satellites.
We observed a GEC increment from 10 to 24% for the storm peak after the Starlink launch at both storms, accompanying the neutral density increase. This characteristic presents a measure of the positive GEC intensification for the second phase of the ionosphere storm.
The different 1-and 2-days 'forecast' of GIMs produced by IZMIRAN, CODE, CASG and BUAG centers is compared with 'true' GEC profiles during two geomagnetic storms on 3-5 February and 7-9 July 2022 when S-36 and S-49 Starlink satellites have been launched at storm time. The NN UPC-ionSAT forecast for 6, 12, 18, 24 and 48 h in advance has been also evaluated for these events.
A numerical estimate of performance of forecasts is made with R-square (R 2 ) and RMS formulae. The monthly estimates of R 2 for February and July 2022 reveal either the acceptable conformity or the difference between the 'true' and 'forecast' GIMs transformed to Global Electron Content metrics. However, a similar estimate for the storm conditions on 3-5 February and 7-9 July 2022 disclosed a failure to reasonably forecast GEC (and GIMs). While the positive R 2 = 1 presents the best conformity of the data we obtained, the negative R 2 for all forecasting results during the storms which characterize unreliable storm-time performance of the forecasting techniques under consideration. The RMS deviations during the storm are greater than those obtained for the total month of February and of July, where the storm conditions are mixed with the dominant quiet times.
The predicted GIMs providing closer forecasted GEC (and detrended GEC) to the now-casted ones are those with horizons at 24 (and 48) h, and from the day after the storm, i.e., once the now-casted GIMs have experienced the starting of the space weather event. The results of this study aim to revisit the GIM prediction, from the GEC perspective, for understanding, firstly, and improving, afterwards, the corresponding forecasting, specially at the subdaily horizons.
Variabilities of the Earth's ionosphere during the storms can adversely affect the spacebased technological infrastructures, such as Low-Earth Orbit (LEO) satellites including the Starlink network and the Global Navigation Satellite System (GNSS). In turn, the GNSS observations and GIMs products provide a ground for the development of reliable GIMs forecasting techniques, which presents a challenge for the satellites' operation during the space weather events.